There are a number of different cellular telephone standards, such as GSM, UMTS, LTE that define different operating frequencies and protocols to allow user equipment (UE), such as a mobile telephone, to communicate with other user equipment via the telephone network. Many UEs are able to operate using a number of these different standards and typically will connect with the network node that provides the best signal strength and the best service level. However, as the UE moves, it has to handover to a different network node, which may operate using a different technology. For example, the UE may initially be connected with an LTE network node and may move out of coverage of that node into the cell coverage of a UMTS network node. Such handover is called “inter-RAT” handover as the UE changes the Radio Access Technology (RAT) during the handover. According to the current 3GPP standards, it is the responsibility of the network nodes to determine when a UE should handover to another network node. The network node makes this decision based on measurements provided by the UE for a number of candidate neighbouring cells (defined in a neighbour cell list) provided to the UE by the network node.
With the number of different technologies supported within a single phone on the increase (i.e. three or more), the task of managing inter-RAT measurements gets ever more complex. The current principle is that the network is all knowing (it knows the theoretical capabilities of the UE and its current state in sufficient detail). So the network should be able to manage traffic gaps (directly or indirectly, according to the technology) to allow inter-RAT measurements to be made by the UE. Moreover, the network assumes that the UE is able to act as planned and expects results within a certain timeframe.
Thus, when the network requires a UE to make inter-RAT measurements, it may define the measurements to be made and set up periodic reporting. In response, the UE makes the measurements during the managed gaps and then in due course, the UE sends measurement reports. It may:                report some measurements;in which case the network might assume that more measurements will be coming, if the report is incomplete (i.e. some cells have not been measured yet).        report no measurements;in which case the network might assume that the UE has completed all its measurements (i.e. any missing cell in the reports is invisible to the UE).        
However, the inventors have realized that these assumptions made by the network are problematic and could be wrong and it may be a waste of effort to try and achieve absolute mastery of the UE's real-time state and capability. For instance the reporting interval provision might have been inappropriate for the UE's actual capabilities and circumstances on the current RAT and the UE might have been unable to do any measurements at all, without that implying that the measurements are complete (i.e. that it definitely cannot use any of the neighbouring cells). This problem could be solved by the network defining a relatively long reporting interval, but this is inefficient.